Uninterruptible power supply systems are apparatuses which generally provide power generated by a battery or an additional auxiliary power supply device to a load in case of emergency such as a power failure. Since an uninterruptible power supply system is allowed to operate in the event of a power outage and an auxiliary power supply device supplies power for several seconds to several hours, electric installations of a load are protected and electric installations are allowed to normally operate.
Such uninterruptible power supply system includes a central processing unit (CPU) which controls operations of converting prevailing alternating current (AC) power into direct current (DC) power to charge an auxiliary power supply device such as a battery, converting DC power of the auxiliary power supply device into AC power to be supplied to a load in the event of an electric discharge, and converting the DC power of the auxiliary power supply device into AC power when a power outage is sensed.
However, the CPU may malfunction due to electromagnetic waves and may wrongly determine as a power outage occurs when it does not occur due to a failure in hardware of the CPU or an error or disorder in software such as an error in a control program of the CPU. Accordingly, the CPU allows DC power of an auxiliary power supply device to be converted into AC power, thereby generating a discharge of the auxiliary power supply device even though a power outage does not occur.
Also, after a power outage actually occurs, since the DC power of the auxiliary power supply device is not converted into AC power before the CPU determines the occurrence of the power outage and begins controlling a conversion operation of the power of the auxiliary power supply device. Accordingly, for example, when the load is one of a network server, a hub forming a local area network (LAN), an L2 switch, an access point, etc. it is impossible to normally perform network communication. Also, when the load is a closed-circuit television (CCTV) camera forming a security system, since security surveillance is not normally performed, unexpected damages may occur to users.
Also, a configuration of a circuit for converting prevailing AC power into DC power to charge the auxiliary power supply device and converting DC power of the auxiliary power supply device into AC power to supply DC power again to the load becomes complicated.